linux-kernel - Re: [PATCH 2/2] cpufreq: cpufreq-cpu0: provide compatibility string for DT matchup

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Date:	Tue, 12 Mar 2013 09:43:34 -0500
From:	Nishanth Menon <nm@...com>
To:	Benoit Cousson <b-cousson@...com>
CC:	Santosh Shilimkar <santosh.shilimkar@...com>,
	<linux-pm@...r.kernel.org>,
	"devicetree-discuss@...ts.ozlabs.org" 
	<devicetree-discuss@...ts.ozlabs.org>,
	<linux-kernel@...r.kernel.org>, cpufreq <cpufreq@...r.kernel.org>,
	"Rafael J. Wysocki" <rjw@...k.pl>, <linux-omap@...r.kernel.org>
Subject: Re: [PATCH 2/2] cpufreq: cpufreq-cpu0: provide compatibility string
 for DT matchup

On 15:28-20130312, Benoit Cousson wrote:
> On 03/12/2013 06:07 AM, Santosh Shilimkar wrote:
> > On Tuesday 12 March 2013 04:35 AM, Nishanth Menon wrote:
> >> commit 5553f9e (cpufreq: instantiate cpufreq-cpu0 as a platform_driver)
> >> now forces platform device to be registered for allowing cpufreq-cpu0
> >> to be used by SoCs. example: drivers/cpufreq/highbank-cpufreq.c
> >>
> >> However, for SoCs that wish to link up using device tree, instead
> >> of platform device, provide compatibility string match:
> >> compatible = "cpufreq,cpu0";
> 
> You cannot add a non-HW relative binding... DT is supposed to represent
> the pure HW.
> AFAIK, cpufreq has nothing to do with the HW definition.
Ref:
https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/drivers/cpufreq/highbank-cpufreq.c#n61
there is a need for a device of some sort.  in the example above, we
register a dummy device for linking up with cpufreq-cpu0 driver.
what we do in this patch is to indicate that SoC CPUs are managed by
cpufreq-cpu0 driver.

I am a bit curious to see how else would we represent drivers to manage
real h/w devices like CPU? Is the highbank style the recommended way to do
things?
> 
> >>
> >> Cc: "Rafael J. Wysocki" <rjw@...k.pl>
> >> Cc: Santosh Shilimkar <santosh.shilimkar@...com>
> >> Cc: Shawn Guo <shawn.guo@...aro.org>
> >> Cc: linux-kernel@...r.kernel.org
> >> Cc: cpufreq@...r.kernel.org
> >> Cc: linux-pm@...r.kernel.org
> >> Cc: linux-omap@...r.kernel.org
> >>
> >> Signed-off-by: Nishanth Menon <nm@...com>
> >> ---
> >>  .../devicetree/bindings/cpufreq/cpufreq-cpu0.txt   |    3 +++
> >>  drivers/cpufreq/cpufreq-cpu0.c                     |    6 ++++++
> >>  2 files changed, 9 insertions(+)
> >>
> > Looks fine to me. CC'ing dt list in case some one has
> > comments on binding updates.
> > 
> > Acked-by: Santosh Shilimkar <santosh.shilimkar@...com>
> 
> Not-Acked-by-me.

-- 
Regards,
Nishanth Menon
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